Synovial effusions of the knee will be sytematically studied in patients with rheumatic diseases. Special attention will be paid to the diagnosis, the volume of the effusion, its hydrostatic and colloid osmotic pressures, its content of glucose, of respiratory gases, and of selected serum proteins and the rate of clearance from the joint of both free and albumin bound radioiodine. From these variables, we expect to draw inferences as to the effective synovial blood flow, the synovial lymph flow, the permeability of the synovium to proteins, the mean hydrostatic pressure within the synovial microvasculature, and the inter-relationships of these parameters. We expect, for instance, that the hydrostatic pressure of effusions will correlate negatively with pH, pO2, glucose concentration, and effective synovial blood flow while correlating positively with pCO2 lactate concentration, and synovial permeability to proteins. Additional studies will compare and contrast the convex and concave sides of synovial joints such as the hip and shoulder. Variables under investigation will include morphology of subchondral bone, flexibility in compression testing, and hydraulic systems of force dispersal. These studies will primarily employ cadaver joints of dogs and pigtailed macaques.